1. Field of the Invention:
This invention relates to mold structures, and more particularly, to a mold structure for use in the molding of an encapsulant for encapsulating a semiconductor chip.
2. Description of Related Art:
Molding process is an important step in IC packaging, in which a set of specially-shaped molding pieces are used for the molding of an encapsulant for encapsulating semi-conductor dies. In use, the molding pieces are attached to each other to define a cavity therewithin; and then, an encapsulating material, typically resin, can be filled into the cavity to form the intended encapsulant.
Conventionally, there are many various kinds of patented mold structures that can be used in the molding of encapsulants, such as the U.S. Pat. No. 5,971,734.
One drawback to the conventional mold structures, however, is that flash would easily occur at the junction between the two molding pieces. This is because that the junction between the two molding pieces would hardly reach the level of absolute airtightness, and consequently, a fissure would be left at the junction. During the molding process, flash occurs if the melted resin enters this fissure. This drawback is further illustratively depicted in the following with reference to FIGs. 1A-1B.
FIG. 1A shows a schematic top view of the mold structure disclosed in the U.S. Pat. No. 5,971,734. As shown, this patented mold structure includes a bottom molding piece 10 and an upper molding piece 20; and when these two molding pieces 10, 20 are attached to each other, it defines a cull 11, a runner 12, a subrunner 13, and a molding cavity 14 therewithin (for detailed description of these parts, please refer to the specification of U.S. Pat. No. 5,971,734). During molding process, melted resin is introduced into the cull 11 and which will then flow through the runner 12 and the subrunner 13 to be guided into the respective molding cavity 14 for the purpose of forming an encapsulant (not shown) in each molding cavity 14.
However, as shown in FIG. 1B, the junction between the bottom molding piece 10 and the upper molding piece 20 would hardly reach the level of absolute airtightness; and consequently, a fissure 30 would be left in the junction. Although this fissure 30 is very small in dimension, it would nevertheless allow a small part of the melted resin used in the molding process to enter therein, thus causing undesired flash into the fissure 30. As roughly illustrated in FIG. 1A, after the molding process is completed, flashed resin would be left around the rims of the cull 11, the runner 12, and the subrunner 13 (the flashed resin is indicated by the reference numeral 15).
To remove the flashed resin, it is required to perform a cleaning process prior to the next round of molding process. However, this cleaning process would undesirably cause the removed resin to be scattered away, thus causing contamination to the nearby fabrication tools, making the removed resin easily attached to the molded encapsulants during the next round of molding process. This would degrade the IC packaging quality.